A.G. Adam

Hyperfine structure in high spin multiplicity electronic states: Analysis of the B 4Π–X 4Σ− transition of gaseous NbO

The (0,0) band of the B 4Π–X 4Σ− transition of NbO, near 6600 A, has been analyzed from spectra taken at sub‐Doppler resolution. The transition is notable for the great width of its Nb nuclear hyperfine structure, which is caused principally by the unpaired 5sσ electron in the ground state interacting with the large magnetic moment of the 4193Nb nucleus (I=9/2). A fit to the ground‐state combination differences, including four very precise microwave lines measured by Suenram et al. [J. Mol. Spectrosc. 148, 114 (1991)], has given a comprehensive set of rotational, spin, and hyperfine parameters. Prominent among these are the third‐order spin–orbit distortions of the spin‐rotation interaction and the Fermi contact interaction, which are large and well determined, reflecting different degrees of spin–orbit contamination of the the 4Σ1/2− and 4Σ3/2− components of the ground state.The δ 2π B 4Π state was hard to fit, for a number of reasons. First, its spin–orbit structure is asymmetric, because of strong pert...

Gas-phase electronic spectroscopy of cobalt monofluoride

Abstract Electronic spectra of the cobalt monofluoride molecule have been observed for the first time. Laser-induced fluorescence in a pulsed molecular beam was used to find several molecular bands between 450 and 540 nm. A CoF ground state vibrational frequency of 662.6 cm−1 was determined using the dispersed fluorescence technique. Three molecular bands, centered at 18780.76 cm−1, have been ronationally assigned and the electronic transition has been determined to be 3Φi-X3Φi. Effective constants for these two states have been obtained by a nonlinear least-squares fit of the data.

A laser‐induced fluorescence study of bands of the red system of gaseous CoO: Evidence for a 4Δi ground state

Three bands of the ‘‘red’’ system of gaseous CoO have been rotationally analyzed using laser‐induced fluorescence techniques. The available evidence indicates that the lower levels are the Ω=7/2 and 5/2 spin–orbit components of a 4Δi electronic state, which is assigned as the ground state of the molecule. The cobalt nuclear hyperfine splittings are small in the ground state, which suggests that no unpaired electron in a σ molecular orbital derived from the Co 4s atomic orbital is present, so that the electron configuration is presumably σ2δ3π2; the ground state bond length (r0) is 1.631 A. The upper electronic levels are heavily perturbed, both rotationally and vibrationally, and their hyperfine structures, though following case (a) behavior, are large and irregular. This work on CoO completes the determination of the ground state symmetries and bond lengths for the whole series of the 3d transition metal monoxides; some comparisons for the members of the series are given.

Vibronic perturbations in the à 2Πu–X̃ 2Πg transition of BO2: K‐resonance crossings and the onset of chaotic behavior

A detailed re‐investigation of the (0,0) and 211 bands of the A 2Πu–X 2Πg transition of 11BO2, near 545 nm, has been carried out from spectra taken at sub‐Doppler resolution. Avoided crossings are found to occur between the 2Σ and 2Δ vibronic components of the v2=1 level of the A 2Πu state. These perturbations are the first known examples of K‐resonance crossings, which result from an interplay of the electronic Λ‐type doubling and the vibrational l‐type doubling in a state where the electrostatic parameter e is small. It turns out that perturbations of this type must always occur in a 2Π electronic state if the ratio A/eω2 is large enough, but have not been seen until now for lack of suitable data. Their existence allows an unusually complete description of the orbital angular momentum effects in both the A 2Πu and X 2Πg states. It has been necessary to fit the avoided crossings by a full matrix treatment of the K resonance. In addition the A 2Πu state, although it appears to be unperturbed at lowe...

The electronic structure of ZrCl

The proposed electronic assignments of our previously reported near infrared transitions of ZrCl [J. Mol. Spectrosc. 186, 335 (1997); 196, 235 (1999)] have been revised following the suggestion of Sakai, Mogi, and Miyoshi [J. Chem. Phys. 111, 3989 (1999)]. The ground state is now assigned as the X 2Δ state followed by the a 4Φ state being the lowest in the quartet manifold. The previously reported transitions [7.3]2Δ–a 2Φ, [9.4]2Φ–a 2Φ, and C 4Δ–X 4Φ are now reassigned to C 2Φ–X 2Δ, E 2Φ–X 2Δ, and d 4Δ–a 4Φ, respectively. The new assignments are supported by our own ab initio calculations. Laser excitation spectra of the 414 nm band system have also been observed at low resolution and are attributed to a 4Γ–a 4Φ transition.

Laser optogalvanic and jet spectroscopy of germylene (GeH2): New spectroscopic data for an important semiconductor growth intermediate

The A 1B1–X 1A1 electronic transition of germylene has been reinvestigated. A room temperature absorption spectrum of the central portion of the 000 band of GeH2 has been obtained using the technique of laser optogalvanic spectroscopy. A rotationally resolved spectrum of the 000 band of jet-cooled GeD2 has been recorded with a pulsed discharge source. Analysis of these spectra has yielded ground and excited state rotational constants for the 74GeH2, 72GeH2, 70GeH2, 76GeD2, 74GeD2, 72GeD2, and 70GeD2 isotopomers and approximate equilibrium structures of: r″(Ge–H)=1.5883(9) A, θ″(H–Ge–H)=91.22(4)°, r′(Ge–H)=1.5471(6) A, and θ′(H–Ge–H)=123.44(2)°. The ground state ν1 and ν2 vibrational frequencies have been determined from wavelength-resolved fluorescence spectra of jet-cooled GeH2 and GeD2. There is good evidence that GeH2 rotational levels with Ka′>1 are so strongly predissociated that lifetime broadening makes them diffuse, severely restricting the information that can be obtained from absorption and las...

Electronic absorption spectroscopy of N2+ using velocity modulation: Rotational structure in the (6, 1) and (13, 6) vibrational bands of the A-X system

The (6, 1) and (13, 6) vibrational bands of the A2Πu-X2Σg+ electronic transition of N2+ have been recorded in absorption, at Doppler-limited resolution, by the technique of velocity modulation. The rotational fine structure was fitted by least squares to standard expressions. The rotational and translational temperatures have been measured and indicate an equilibrium between translational and rotational motion of N2+ in the HeN2 plasma.

A precise calibration system for high‐resolution visible‐laser spectroscopy

A method for calibrating high‐resolution laser spectra in the visible is described. The system is based on an evacuated Fabry–Perot etalon whose cavity length is servolocked to a stabilized HeNe laser; the absolute order number of the fringe at the HeNe frequency is known and the free spectral range can be determined with high accuracy. For absolute‐frequency measurements the order number of a transmission fringe is obtained from a commercial wavemeter (whose accuracy is sufficient to identify the fringe); the absolute frequency is then the HeNe frequency multiplied by the ratio of the ‘‘unknown’’ order number to the ‘‘lock‐point’’ order number. The long‐term frequency reproducibility of the system is better than 25 MHz. Small‐frequency splittings such as molecular hyperfine intervals can be measured to ±1 MHz, while large‐frequency intervals (of the order of 500 GHz) are consistent to better than 10 MHz.

The first observation of the rhodium monofluoride molecule: Jet-cooled laser spectroscopic studies

Rhodium monofluoride has been observed and spectroscopically characterized. RhF molecules were produced under jet-cooled conditions in a laser vaporization molecular beam source by the reaction of a laser-vaporized rhodium plasma with SF(6) doped in helium, and studied with laser-induced fluorescence spectroscopy under both medium and high resolution. More than 25 bands have been observed in laser-induced fluorescence between 18,500 and 24,500 cm(-1) and five of these have been recorded at 200 MHz resolution. All bands of appreciable intensity have been rotationally analyzed. The ground electronic levels has Omega=2, which is attributed to an inverted (3)Pi state from the 2 delta(4)6 pi(3)12 sigma(1) electron configuration. The ground level rotational constants are B=0.272 45 cm(-1), D=1.035 x 10(-7) cm(-1). Very small ground level Lambda doublings are evident in the spectrum. Excited states having Omega=1, 2, and 3 have been identified. Dispersed fluorescence spectroscopy from 11 excited levels has been used to locate a large number of low-lying vibronic states within the energy range up to 8,000 cm(-1). A ground state vibrational interval of approximately 575 cm(-1) is suggested.

High resolution laser induced fluorescence spectroscopy of the [18.8]Φi3−XΦi3 (0,0) band of cobalt monofluoride

The fine and hyperfine interaction parameters in the [18.8]Φ3 (υ=0) and XΦ3 (υ=0) states of cobalt monofluoride, CoF, have been determined from an analysis of high-resolution laser induced fluorescence spectra of the [18.8]Φ33−XΦ33 and [18.8]Φ43−XΦ43 band systems. The previously reported pure rotational transitions of the XΦ43(υ=0) state [T. Okabayashi and M. Tanimoto, J. Mol. Spectrosc. 221, 149 (2003)] were included in the data set. The hyperfine parameters for Co59 (I=7∕2) and F19 (I=1∕2) have been interpreted using atomic data together with a proposed molecular orbital description for the [18.8]Φi3 and XΦi3 states. A comparison of the hyperfine parameters in the XΦ3 state of cobalt monohydride, CoH, with those of the XΦ3 state of CoF reveals that the bonding in the two molecules is significantly different. It is shown that, in a situation where the Ω substates of a multiplet degenerate electronic state are analyzed separately, the Fermi contact parameter b can be determined with fair accuracy from the...